The present invention relates to a parking brake system having a brake cylinder and brake piston. A parking brake system of this type is known from the general prior art and, in particular, from DE 10 2011 105 068 A1. Furthermore, the invention relates to a transmission having a parking brake system of this type, and to a motor vehicle having a transmission of this type.
In the following text, the invention will be described in conjunction with what is known as a parking lock for a passenger motor vehicle automatic transmission; this is not to be understood to be a restriction of the invention to an application of this type.
Motor vehicles having an automatic transmission are usually equipped with what is known as a parking lock mechanism, in order to prevent the vehicle from rolling away at a standstill of the vehicle or in the case of a switched-off engine. Depending on the transmission design, the actuation of the parking lock can take place manually via a selector lever or hydraulically by a parking lock actuator. Said parking lock actuator can be a brake cylinder with a brake piston, it being possible for the brake cylinder to lock/block a transmission output via the brake piston, in particular in a positively locking manner, and rolling away of the vehicle therefore being prevented.
DE 10 2011 105 068 A1 has disclosed that the hydraulic brake piston can be fixed in a defined position by way of a locking apparatus. Said fixing action can be canceled by way of an electromechanical actuator or by way of a hydraulic or pneumatic actuator, as a result of which the brake piston can be moved.
It is an object of the invention to specify a parking brake system with improved operational reliability.
A parking brake system according to the invention has a brake cylinder with a brake piston. Furthermore, the brake cylinder is preferably configured as a single-acting hydraulic cylinder and preferably has a piston spring which is set up to move the brake piston in one direction. The piston spring further preferably acts on the brake piston in such a way that the latter is pressed into a braking position (blocked transmission), and a failsafe system can thus be achieved, in particular. The brake piston is mounted in the brake cylinder such that it can be moved between a braking position, in which at least one transmission output shaft is blocked, and a locking or releasing position, in which the transmission output shaft can be rotated.
The parking brake system has a piston lock for fixing the brake piston in at least one position, in particular in the locking or releasing position.
Locking or fixing of the brake piston is to be understood to mean, in particular, that the brake piston is prevented from leaving said position by way of the piston lock in a positively locking or frictionally locking manner. Said piston lock can preferably be connected in a fluid-conducting manner to a locking valve.
The brake cylinder can further preferably be connected in a fluid-conducting manner to a brake valve.
The locking valve is set up to actuate the piston lock by way of a hydraulic fluid, that is to say to load it by way of a hydraulic pressure and, as a result, to transfer it from an operating state, in which the brake piston is locked, into an operating state, in which the brake piston is not locked and can therefore be moved, or vice versa. The piston lock further preferably has at least one (preferably single-acting) hydraulic cylinder.
The piston valve preferably has a valve connector on the side which faces away downstream from the brake piston, which valve connector can be connected in a fluid-conducting manner to a supply pressure system. Here, in the context of this invention, downstream is to be understood to mean the flow direction from the piston valve toward the brake cylinder or from the locking valve toward the piston lock.
According to the invention, the locking valve has a valve connector on the side which faces away downstream of the piston lock, which valve connector can be connected in a fluid-conducting manner to said supply pressure system. The result of said arrangement of the valve connectors on the locking valve and on the piston valve is that the two valves are arranged downstream parallel to one another. The locking valve can therefore be connected in a fluid-conducting manner directly to the supply pressure system. Here, in this context, “can be connected directly” is to be understood to mean, in particular, that the pressure from the supply pressure system is not fed via the piston valve to the locking valve.
In particular, the parallel nature of the two valves makes it possible to actuate said two valves autonomously from one another and therefore to increase the operational reliability of the parking brake system.
In one preferred embodiment, the piston valve is configured as a directional valve. A directional valve of this type has at least three valve connectors and at least two control positions. The piston valve is preferably configured as a 3/2-way valve, and preferably as a 4/2-way valve with four valve connectors and two control positions. Here, control positions are to be understood to mean positions of an internal valve slide, by way of which positions the valve connectors which are arranged downstream on different sides of the directional valve can be connected to one another in a selective manner. Directional valves of this type are known from the prior art, in particular as longitudinal slide valves or rotary slide valves.
The locking valve is further preferably also configured as a directional valve which has at least three valve connectors and at least two control positions.
The piston valve which is configured as a 3/2-way valve further preferably has a valve connector downstream on the side which faces the brake cylinder, and two valve connectors on the downstream opposite side of the piston valve. One of said two valve connectors can be connected in a fluid-conducting manner to the supply pressure system, and the further of the two valve connectors can be connected in a fluid-conducting manner to a hydraulic reservoir, in particular a hydraulic oil tank or the transmission oil sump.
The piston valve which is configured as a 4/2-way valve further preferably has two valve connectors downstream on the side which faces the brake cylinder, and two further valve connectors on the downstream opposite side of the piston valve. A piston valve of this type is preferably used for a double-acting brake cylinder, it preferably being possible for the two valve connectors on that side of the piston valve which faces the brake cylinder downstream to be connected to separate connectors of the brake cylinder. The valve connectors of the piston valve which face the supply pressure system downstream are further preferably connected as in the case of the 3/2-way valve.
The supply pressure system is preferably to be understood to mean a hydraulic circuit for supplying the parking brake system with a hydraulic fluid, preferably with hydraulic oil and with preference with transmission oil.
The locking valve is preferably configured as a directional valve, and the locking valve is preferably configured as a directional valve and has at least two control positions and three valve connectors. Two of said three valve connectors are preferably arranged on that side of the locking valve which faces the supply pressure system downstream. The third valve connector is further preferably arranged on the downstream opposite side of the locking valve.
The locking valve or the piston valve or both valves preferably has/have at least one control pressure connector. Within the context of the invention, a control pressure connector is to be understood to mean a connector on one of the valves, via which connector said valve can be loaded with a pressurized hydraulic medium at a control pressure, with the result that, in particular, the control position of the valve can be changed or influenced. Here, said control pressure is provided, in particular, to transfer the valve from the one of its control positions into the other or to secure said valve in the control position which has already been assumed.
At least one of the two valves (locking valve, piston valve) further preferably has two or more control pressure connectors. Each of said two valves further preferably has in each case two control pressure connectors. A particularly simple type of controlling the parking brake system is made possible, and therefore its operational reliability can be increased, in particular by way of the loading of the locking valve and/or the piston valve by way of at least one control pressure.
In one preferred embodiment, a shut-off valve, preferably a check valve, with preference a threshold value valve, is arranged downstream between the locking valve and the piston lock. Here, said shut-off valve is provided to prevent the throughflow from the piston lock in the direction of the locking valve. The throughflow through said shut-off valve in the opposite direction is preferably made possible only when the pressure of the hydraulic fluid which is situated between the locking valve and the shut-off valve exceeds a predefined locking threshold value. Said locking threshold value can further preferably be preset or defined.
A tank return line with a throttling valve is further preferably provided downstream of the check valve or threshold value valve and upstream of the piston lock, via which tank return line hydraulic fluid can be discharged into the hydraulic reservoir. The locking threshold value can further preferably be set or predefined via said throttling valve. In particular, a shut-off valve of this type with a locking threshold value makes it possible to prevent the piston lock from being canceled due to faulty control of the locking valve.
A tank return line with a throttling valve is further preferably provided downstream of the check valve or threshold value valve and upstream of the piston lock, via which tank return line hydraulic fluid can be discharged into the hydraulic reservoir. A maximum actuating pressure for the piston lock can further preferably be set via said throttling valve.
In one preferred embodiment, at least one of the control connectors of the piston valve can be connected in a fluid-conducting manner to at least one of the control connectors of the locking valve. Pressure differences in the control connectors can be equalized by way of a connection of this type, and tests have shown that the operational reliability of the parking brake system can therefore be increased.
In one preferred embodiment, the motor vehicle transmission has at least one start-up element which has a start-up pressure connector. Via said start-up pressure connector, the start-up element can be loaded with a start-up pressure and can thus be transferred from an operating state, in which no torque is transmitted by the start-up element, into an operating state, in which a torque can be transmitted, or vice versa. A start-up element of this type is preferably to be understood to mean a clutch or a torque converter which is arranged in relation to the transmission of power between an internal combustion engine and a transmission, in which the parking brake system is preferably arranged. The start-up element is further preferably also to be understood to mean a converter lock-up clutch.
In one preferred embodiment, the motor vehicle transmission has at least one shifting device or one shifting element which is set up to bring about a gear change in the motor vehicle transmission, that is to say, in particular, a gear shift from the n-th gear into the n+1-th gear or vice versa. To this end, the shifting device can further preferably be loaded with a shifting pressure via a shifting pressure connector. Different shifting devices can further preferably be loaded with different shifting pressures. At least one of the control connectors of the locking valve or the piston valve can preferably be connected in a fluid-conducting manner to the shifting pressure connector. A shifting element of this type or a shifting device of this type is further preferably to be understood to mean a clutch, a synchronizer or a brake, as are usually used in automatic transmissions or automated transmissions for selectively establishing a torque-connecting connection during the gear change.
In one preferred embodiment, the locking valve can be loaded by way of a prestress spring. Here, the prestress spring is preferably brought about by way of a valve spring device and causes a spring actuating force on the valve. In particular, the locking valve can be moved into a first control position by way of said spring actuating force. Said spring actuating force further preferably acts at least on the locking valve or on a valve slide in said locking valve in such a way that it is loaded with a force in the direction of the first control position.
The locking valve can preferably be loaded with a control pressure via the control connector which can be connected in a fluid-conducting manner to the start-up pressure connector. Said control pressure brings about a pressure actuating force in the locking valve, which pressure actuating force acts in the same direction as said spring actuating force. At least one component of the pressure actuating force preferably acts in the same direction as the spring actuating force.
The locking valve can further preferably be loaded with a second control pressure via the control connector which can be connected in a fluid-conducting manner to the shifting pressure connector. A second pressure actuating force is brought about in the locking valve by way of said second control pressure, which second pressure actuating force acts in the opposite direction to the spring actuating force. At least one component of the second pressure actuating force preferably acts in the opposite direction to the spring actuating force.
In one preferred embodiment, the piston valve can be loaded by way of a prestress spring, preferably the valve slide which is arranged in the piston valve. A piston spring actuating force is preferably brought about by way of said prestress spring. The piston valve can be moved into a first control position by way of said piston spring actuating force.
In one preferred embodiment, the piston valve can be loaded with a first piston control pressure via the control connector which can be connected in a fluid-conducting manner to the start-up pressure connector. A pressure actuating force can preferably be brought about on the piston valve or on the valve slide of the piston valve by way of said piston control pressure. Said pressure actuating force preferably acts in the opposite direction to the piston spring actuating force.
In one preferred embodiment, the piston valve can be loaded with a second piston control pressure via the control connector which can be connected in a fluid-conducting manner to the shifting pressure connector. A second piston pressure actuating force can preferably be brought about by way of said second piston control pressure. The active direction of the second piston pressure actuating force is further preferably opposed to that of the piston spring actuating force; at least one component of the piston pressure actuating force is preferably opposed to the piston spring actuating force.
The parking brake system according to the invention can be used in an automated manual transmission or in an automatic transmission in such a way that a rotational movement, at least of the transmission output shaft, can be blocked by way of the parking brake system.
Transmissions having known parking brake systems are known; the functional reliability of a transmission of this type can be increased, in particular, by way of the parking brake system according to the invention. A plurality of shifting elements (clutches, brakes) which can be loaded with one hydraulic pressure or with different hydraulic pressures for control purposes are preferably provided in a transmission of this type for changing the gears.
A transmission of this type further preferably has a start-up element, in particular a start-up clutch or a torque converter, in particular with a lock-up clutch. The hydraulic pressures, with which said start-up element and at least one, preferably two or with preference a plurality of said shifting elements can be loaded, are used for controlling preferably the piston valve, with preference the locking valve, and particularly preferably both valves.
A vehicle, in particular a passenger motor vehicle, further preferably has the automated manual transmission or automatic transmission according to the invention.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.